Various business critical applications may run on virtual machines and thus it may be critical to create backups of such virtual machines in case a failure or loss of data occurs. Backups of virtual machines may be performed often and may consume valuable resources causing the virtual machine to run slower. In some circumstances, it may be necessary to backup only data or sectors which have changed in the virtual machine since a previous backup. Determining the changed data or sectors may require a reading of the entire virtual machine disk, which may be time-consuming.